linux-kernel - [PATCH] spi: omap2-mcspi: Ensure that CS is correctly asserted when switching from MULTI mode to SINGLE mode

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Date: Tue, 09 Apr 2024 19:25:33 +0200
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Mark Brown <broonie@...nel.org>
Cc: linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org, 
 miquel.raynal@...tlin.com, thomas.petazzoni@...tlin.com, 
 yen-mei.goh@...sight.com, jeremie.dautheribes@...tlin.com, 
 Louis Chauvet <louis.chauvet@...tlin.com>
Subject: [PATCH] spi: omap2-mcspi: Ensure that CS is correctly asserted
 when switching from MULTI mode to SINGLE mode

The OMAP2 support features a "multi" mode, where the controller
automatically sets the Chip Select (CS) when necessary. This mode allows
for shorter delays between CS selection and word content, but the CS is
always deasserted at the end.

The default transfer_one_message function expects the last transfer of a
message to keep the CS enabled. However, when two consecutive messages
use "multi" mode followed by "single" mode, the chipselect is not enabled
during the second message. This discrepancy causes the driver to time
out.

To address this issue, the CS is now reasserted for each new message that
follows a "multi"-mode message. This change ensures proper CS handling
and prevents driver timeouts.

Fixes: d153ff4056cb ("spi: omap2-mcspi: Add support for MULTI-mode")

Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
---
 drivers/spi/spi-omap2-mcspi.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/spi/spi-omap2-mcspi.c b/drivers/spi/spi-omap2-mcspi.c
index 7e3083b83534..571e4499f71c 100644
--- a/drivers/spi/spi-omap2-mcspi.c
+++ b/drivers/spi/spi-omap2-mcspi.c
@@ -1264,6 +1264,15 @@ static int omap2_mcspi_prepare_message(struct spi_controller *ctlr,
 	struct spi_transfer	*tr;
 	u8 bits_per_word;
 
+	/*
+	 * When the last transfer used multi-mode, the CS is not keep down by the controller.
+	 * The default transfer_one_message expect that the last transfer of a message keep the CS
+	 * active.
+	 * Ensure that the next call to spi_set_cs will work as expected if single-mode is used.
+	 */
+	if (mcspi->use_multi_mode)
+		master->last_cs = -1;
+
 	/*
 	 * The conditions are strict, it is mandatory to check each transfer of the list to see if
 	 * multi-mode is applicable.

---
base-commit: 51244b7df2f236cea87a10729d5cbc777d199e19
change-id: 20240408-fix-omap2-mcspi-a6b41142ad9a

Best regards,
-- 
Louis Chauvet <louis.chauvet@...tlin.com>